TITLE:   GCN CIRCULAR
NUMBER:  21007
SUBJECT: Konus-Wind observation of GRB 170409A
DATE:    17/04/10 12:43:23 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The long, very bright GRB 170409A (Fermi-LAT detection: Longo et al.,
GCN 21004; Fermi-GBM detection: Burns et al., GCN 21005)
triggered Konus-Wind at T0=9741.024 s UT (02:42:21.024)

The burst light curve shows multiple partially overlapped
emission peaks in the interval from ~T0-29 s to ~T0+95 s.
A possible precursor is seen as a weak count rate excess in
the same KW detector at ~T0-143 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(5.7 ± 0.2)x10^-4 erg/cm2 and a 64-ms peak energy flux,
measured from T0+12.982, of (1.00 ± 0.06)x10^-4 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+91.648 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.76 (-0.05,+0.05),
the high energy photon index beta = -2.23 (-0.11,+0.09),
the peak energy Ep = 808 (-65,+69) keV,
chi2 = 111/95 dof.

The spectrum near the peak count rate (measured from T0+12.288 s
to T0+13.056 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.60 (-0.06,+0.07),
the high energy photon index beta = -3.52 (-6.48,+0.65),
the peak energy Ep = 1671 (-180,+192) keV,
chi2 = 99/77 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170409_T09741/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.